Method of accelerating the hardening of plastic materials



Patented June 9, 1931 ALBERT BRUND AND HELGE BOHLIN, OF HARNOSAND, SWEDEN METHOD OF ACGELERATING THE HARDENING OF PLASTIC MATERIALS No Drawing. Application filed April 16, 1930, Serial No. 444,863, and in Germany April 5, 1928.

Application has been filed in Germany April 5, 1928, and Sweden April 3, 1929.

Themain objects of this invention are to provide an improved method of accelerating the hardening of concrete, mortar and similar coalescent material; and to provide an improved method of this kind which will require only a very small amount of apparatus.

The most common method heretofore in use for the hardening of concrete and similar material has been to merely permit the mass to stand untouched until it has properly set. Such a method has been very objectionable because it consumed a comparatively long time and required very favorable atmospheric and temperature conditions. Concrete, for instance, usually requires twenty-eight days under favorable temperature conditions for attaining that degree of strength which is necessary for construction work.

The improved method which we have discovered greatly accelerates the time required for the proper hardening and produces a more" favorable temperature condition in the mass than that obtained heretofore.

' sistance of the mass.

Our improved method primarily consists in passing an electric current, preferably alternating current, through the plastic mass. By reason of the heat generated in the mass by the electric current, the setting is greatly accelerated. As a result of many experiments, we have determined that with this improved method, after the mass' has been-subjected to the electric current for only a few hours, it

reaches a degree of coalescence which is al-1 most seventy per cent. as great as it would be after a period of twenty-eight days of hardening with prior methods.

In carrying out this invention, the concrete orother substance is poured into the mold. The mold mut'be provided with electrodes placed in any suitable position within the mass. If the concrete is provided with the customary metal reinforcing bars, such bars may be used as the electrodes.

With this-improved method, it is possible to definitely control the hardening process by regulating the electric current while observing the temperature and electrical re- During the hardening process, the electrical resistance of the mass increases steadily. Therefore, the resistance of the mass at any given moment will indicate the progress of the hardening.

During the use of this improved method,

greatest current will have the highest temperature and'consequently the highest electrical resistance because the resistance increases with the temperature. The current will therefore flow toward the portions of less resistance with the result that those portions will rise in temperature, thereby tending to preserve a uniform temperature throughout the entire mass. This uniformity of temperature throughout the entire mass has not been attainable with prior methods of hardening. I

In carrying out this invention, it may be desirable to use metal plates as electrodes while in other cases it may be desirable to emplo the concrete reinforcing bars.

S ilbstantiallythe only apparatus which is necessary to carry out this improvedprocess comprises a transformer, conductors, and electrodes, which are much cheaper to acquire and maintain than the boilers, pipe systems, steam chambers, etc., used in other methods.

Experiments have shown that the consumption of electricity in carrying outzthis method is between thirty and fifty Kwh. per cubic meter of mass. If'desired the molds may be heat insulated and also covered to prevent evaporation of the water.

We claim: The method of accelerating the hardening of a plastic mass having water therein which consists in passing an electric alternating current therethrolulgh. Signed at arnosand, this 27th day of March,-1930.

' .ALBERT BRUND. HELGE BOHLIN. 

